body{
    margin: 0;/* 外边距 0不用给单位 */
    padding: 0;
    min-width: 100%;
    min-height: 100vh;
    color: #295287;
}
.big_box{
    display:flex;
}
.wrap{
    width: 20%;
    height: 100vh;
    background-color:#4b6383;
    overflow:auto;
}
.seg {
    height: 1px;
    width: 100%;
    background-color: black;
}
.item a {
    display: block;
    width: 100%;
    height: 50px;
    color: white;
    text-decoration: none;
    text-align: center;
    line-height: 50px;
    font-size: 20px;
}
.item a:hover{
    color: #FFFFFF;
    background-color: #15305a;
}
.item_title{
    display: block;
    width: 100%;
    height: 50px;
    color: white;
    text-decoration: none;
    text-align: center;
    line-height: 50px;
    font-size: 25px;
}
.homepage{
    margin-left: 15%;

}
.homepage h1{
    color:#4b6383;
    margin-left: 50px;
    font-size: 30px;
}
.header{
    background-color: #4b6383;
    text-align: center;
    color:white;
    font-size: 18px;
    height:38px;
    padding-top:5px;
}
.exit{
    font-size: 15px;
    color:white;
    float:right;
    margin-right: 20px;
}
.button{
    background-color: #308ad9;
    color:white;
    border: 3px solid #308ad9;
    border-radius: 5px;
}
.student_list{
    margin-left: 30px;
}
.student_list h1{
    font-size: 25px;
    margin-left: 10px;
}
table{
    border-collapse: collapse;
    border:2px solid #295287;;
    margin-left:10px;
}
.table th,td{
    border:1px solid #295287;;
    border-spacing: 15px 15px;
}
.a{
    margin-left: 10px;
}
.xsck{
    margin-top: 10px;
}